1. Field of the Invention
This invention relates to an ultrasonic diagnostic apparatus in a type of digital scan converter.
2. Description of the Prior Art
Among conventional ultrasonic diagnostic apparatuses for transmitting ultrasonic beams to scan an object under investigation at a scanning rate of about 250 .mu.sec and for forming a tomographic image or tomogram of the object in accordance with reflected ultrasonic echoes from the object, an apparatus of the type called "digital scan converter" has recently been developed. Such an apparatus is described, for example, in U.S. Pat. No. 4,423,737 issued on Jan. 3, 1984 to Yano.
Various types of conventional ultrasonic scan modes such as linear scan, sector scan and convex scan have been proposed.
In a digital scan converter type apparatus, echo signals received from the transducer are converted to digital echo signals which are then temporarily stored in a memory, such as a frame memory. Thereafter, the digital echo signals are read out from the memory. In this case, an address for accessing a predetermined memory cell in the frame memory is produced in accordance with a control signal called "vector data". The vector data is required to determine a memory location in a memory in accordance with vector information (i.e., in association with a scanned portion of the object which is represented by the received echo signals). When the echo signals are obtained by, for example, the sector scanner, predetermined addresses are generated in accordance with position and angle data (i.e., vector data) at the respective portions inside the object (however, in practice, this vector data corresponds to position and angle data of ultrasonic beams transmitted from the scanner). The received echo signals are stored in the frame memory in response to these addresses. As a result, a distribution of the memory locations storing the echo signals becomes a "sector".
Demand has arisen recently to use the abovementioned ultrasonic diagnostic apparatus together with a blood current measurement/display device. In this case, blood flow measurement at a high flow rate is also required. In order to satisfy this need, the ultrasonic beams must be transmitted/received at a high scanning rate.
However, no conventional single-digital-scan-converter-type ultrasonic diagnostic apparatus has been proposed to provide multifunctional scanning modes. In addition, no conventional ultrasonic diagnostic apparatus which can be used in combination with another diagnostic apparatus, such as a blood flow measurement/display device, has ever been proposed.
It is therefore an object of this invention to provide an ultrasonic diagnostic apparatus which performs such multifunctions as linear scanning, the sector scanning, convex scanning, trapezoidal scanning and so on, and also is adapted to combine with another diagnostic apparatus, such as a blood flow measurement device.